The present invention relates to a voltage regulator and more specifically to a voltage regulator suitable for a field-programmable gate array (FPGA) semiconductor device. It is contemplated that programming of the device is to be accomplished by application of a programming voltage to several of several thousand fuse elements on the device.
FPGAs provide extreme flexibility in implementing an electrical circuit because the logical interconnection of logic elements can be configured without additional fabrication process steps. Indeed, FPGAs can be configured with a small programming box consisting of little more than a computer controlled high voltage generator. Accordingly, because of the ease in changing the logical configuration of the logic elements, FPGAs are recognized as a time and resource efficient method for verifying the design of the electrical circuit.
However, for FPGAs using low resistance polysilicon or amorphous silicon fuses, the operation of the device at normal operating voltage can induce stress that will ultimately alter the resistance of the fuses and cause the device to operate improperly. As a consequence, there is a constraint on the magnitude of the power supply voltage applied to the core or nucleus logic elements. It is thus necessary to ensure that the power supply voltage is sufficient to properly operate the FPGA device without unnecessarily inducing stress to the fuses. However, to ensure the FPGA is field programmable, provisions must be made that permit the application of a programming voltage to the core logic. What is needed is a voltage regulator for a FPGA that is capable of regulating the core or nucleus logic power supply while permitting field programming of the device.